LONDON (AFP) — UK Prime Minister Keir Starmer on Sunday warned that European security faces a once-in-a-generation moment at the start of Ukraine crisis talks in London, just days after a Kyiv-Washington clash.

Eighteen allies gathered on the key question of security guarantees for Ukraine, especially after US President Donald Trump berated his Ukrainian counterpart, Volodymyr Zelensky, in an unprecedented White House blow-up.

Summit host Starmer, sitting next to Zelensky and in front of the flags of Ukraine and European nations, said it was “a once-in-a-generation moment for the security of Europe and we all need to step up.”

“I hope you know that we are all with you and the people of Ukraine for as long as it takes. Everyone around this table,” he told the Ukrainian leader.

Zelensky was embraced by some of the 18 other top leaders, including Starmer, Canadian Prime Minister Justin Trudeau and NATO chief Mark Rutte.

It was a stark contrast to Zelensky’s unusually heated Friday meeting with Trump in Washington, where he was berated by the American leader and accused of not being “ready” for peace with Russia.

Speaking ahead of the summit in London, Starmer said “nobody wants to see” scenes like Zelensky and Trump’s Oval Office clash.

“We have to find a way that we can all work together. Because, in the end, we’ve had three years of bloody conflict. Now we need to get to that lasting peace,” Starmer told the BBC.

Italian Prime Minister Giorgia Meloni echoed the sentiment, saying as she met Starmer in his Downing Street home that it was “very, very important that we avoid the risk that the West divides.”

Ukraine’s allies have been underscoring their steadfast commitment to counter growing concerns that Trump is about to sell Kyiv short in negotiations with Russia.

Starmer warmly welcomed Zelensky to the British capital on Saturday, the day after the Ukrainian leader was kicked out of the White House, extending a loan to strengthen Ukraine’s depleted defenses.

The London meeting brings together leaders from around continental Europe, including France, Germany, Denmark and Italy as well as Turkey, NATO and the European Union.

With fears growing over whether the United States will continue to support NATO, the meeting will also address the need for Europe to increase defense cooperation.

In addition to attending the security summit, Zelensky is also due to meet King Charles III during his visit.

As Zelensky’s convoy swept into London on Saturday, a crowd of supporters cheered.

“You’re very, very welcome here in Downing Street,” Starmer told Zelensky before their 75-minute closed-door talks.

Zelensky effusively thanked Britain and its people “for their tremendous support from the very beginning of this war.”

The pair unveiled a £2.26-billion ($2.84 billion) loan agreement to support Ukraine’s defense capabilities, to be paid back with the profits of immobilized sovereign Russian assets.

Just a day earlier, Zelensky had been shouted down at the White House.

As cameras rolled in the Oval Office, Trump and US Vice President JD Vance angrily accused Zelensky of not being “thankful” and refusing to accept their proposed truce terms.

Trump has alarmed Kyiv and European allies with his abrupt pivoting of Washington’s years-long support for Ukraine.

The recently inaugurated Republican has cast himself as a mediator between Putin and Zelensky and has sidelined Kyiv and Europe while pursuing rapprochement with Putin.

Though he refused to apologize after the White House clash, Zelensky indicated that he was still open to signing a deal on Ukraine’s mineral wealth — coveted by Trump.

“Despite the tough dialogue,” Ukraine and the United States will “remain strategic partners,” Zelensky said.

“But we need to be honest and direct with each other to truly understand our shared goals,” the Ukrainian leader wrote on X.

Moscow, meanwhile, branded Zelensky’s Washington trip a “complete failure.”

The Kremlin said in remarks aired on Sunday that the United States’s dramatic shift in foreign policy toward Russia largely aligned with its vision.

“The new administration is rapidly changing all foreign policy configurations. This largely coincides with our vision,” Kremlin spokesman Dmitry Peskov said in an interview with Russian state television recorded on Wednesday.